EXCHANGE 


TIlntversitE  of  Cbicago 


I.  The  Three  Nitro-Triphenylamines 

II.  The  Oxidation  of  Diaminophenols 


A  DISSERTATION 

SUBMITTED  TO  THE  FACULTY 

OF  THE  OGDEN  GRADUATE  SCHOOL  OF  SCIENCE 

IN  CANDIDACY  FOR  THE  DEGREE  OF 

DOCTOR  OF  PHILOSOPHY 


DEPARTMENT  OF  CHEMISTRY 


BY 

LOUIS  MELVIN  LARSEN 


Private  Edition,  Distributed  by 

THE  UNIVERSITY  OF  CHICAGO  LIBRARIES 

CHICAGO,  ILLINOIS 

1921 


tftniverstts  ot  Gbtcago 


I.  The  Three  Nitro-Triphenylamines 

II.  The  Oxidation  of  Diaminophenols 


A  DISSERTATION 

SUBMITTED  TO  THE  FACULTY 

OF  THE  OGDEN  GRADUATE  SCHOOL  OF  SCIENCE 

IN  CANDIDACY  FOR  THE  DEGREE  OF 

DOCTOR  OF  PHILOSOPHY 


DEPARTMENT  OF  CHEMISTRY 


BY 

LOUIS  MELVIN  LARSEN 


Private  Edition,  Distributed  by 

THE  UNIVERSITY  OF  CHICAGO  LIBRARIES 

CHICAGO,  ILLINOIS 

1921 


I  •   •        •       • 


I. 

THE  THREE  NITRO-TRIPHENYLAMINES.* 

(i)    Theoretical  Part. 

Hitherto,  only  one  mono-nitro  derivative  of  triphenylamine  has  been 
known;  it  was  prepared  by  Herz1  in  the  year  1890  by  the  treatment  of 
triphenylamine  with  nitric  acid.  Although  this  method  of  preparation 
contains  no  proof  as  to  whether  it  is  an  ortho,  a  meta,  or  a  para  derivative 
it  was,  nevertheless,  listed  in  the  literature  as  the  para.  For  a  purpose,2 
which  will  be  discussed  later,  Piccard  and  Kharasch  needed  the  p-nitro- 
triphenylamine.  Since  we  could  not  find  in  the  literature  any  proof  for 
the  constitution  of  the  compound  prepared  by  Herz,3  nor  a  general  method 
for  the  preparation  of  the  nitro-triphenylamines,  we  tried  to  prepare 
^-nitro-triphenylamine  by  the  introduction  of  phenyl  groups  into  ^-nitran- 
iline.  The  substance  thus  produced  was  indeed  identical  with  the  product 
prepared  by  Herz.  Against  our  proof,  however,  the  objection  could  be 
raised,  that  a  rearrangement  might  have  taken  place  in  the  course  of  the 
reaction  (heating  for  30  hours  at  200°  in  the  presence  of  potassium  car- 
bonate). Were  this  last  objection  valid,  then  we  could  not  obtain,  when 
starting  from  the  three  mono-nitranilines,  three  different  mono-nitro- 
triphenylamines.  Hence  we  phenylated  o-  and  w-nitraniline  as  well  as 
^-nitraniline,  and  obtained  three  isomeric  mono-nitro- triphenylamines. 
Absolute  proof  is  thus  given  that  our  three  derivatives  are,  respectively, 
the  ortho,  the  meta,  and  the  para  compounds. 

Irma  Goldberg4  has  introduced  the  use  of  phenyl  iodide  for  the  prepara- 
tion of  triphenylamine  and  some  of  its  substitution  derivatives.  She 
heated  diphenylamine  with  phenyl  iodide  and  potassium  carbonate  in 
nitrobenzene  solution  in  the  presence  of  some  copper  powder.  The  latter 
had  already  been  used  for  similar  condensations  as  a  catalytic  reagent. 
Since  Kahlbaum  had  introduced  under  the  name  "Kupferbronze"  or 
"Naturkupfer  C,"  a  very  good  preparation  made  by  powdering  metallic 
copper  in  a  special  manner,  no  one  in  the  past,  it  seems,  prepared  the  cop- 

*  This  work  was  published  by  Jean  F.  Piccard  and  Louis  M.  Larsen  in  the  Journal 
of  the  American  Chemical  Society,  39,  2006-2009  (1917). 

1  Ber.,  23,  2537   (1890). 

2  For  the  identification  of  nitroso-triphenylamine. 

3  When  this  article  was  ready  for  publication,  we  happened  to  find  that  Gamborian 
(Ber.,  41,  3510  (1908))  had  already  prepared  the  />-nitro-triphenylamine  by  heating 
together  diphenylamine  and  £-iodo-nitrobenzene  from  which  it  follows  that  its  struc- 
ture is  the  para.     This  reference  is  not  given  in  Richter's  "Lexikon"  of  1911. 

4  Irma  Goldberg,  when  making  o-nitro-diphenylamine  by  heating  in  this  manner 
o-nitraniline  with  phenyl  iodide,  obtained,  in  addition  to  tarry  by-products,  a  mixture 
consisting  of  unchanged   o-nitraniline,   o-nitro-diphenylamine,   and  o-nitro-triphenyl- 
amine.     She  did, not,  however,  isolate  the  last  substance.     Ber.,  40,  4542  (1907). 


per  powder  for  himself.  Being  unable  to  secure  at  this  time  the  German 
product,  we  tried  a  new  chemical  method  for  making  it,  and  we  are  glad  to 
say  that  it  is  possible  to  make  in  this  country  a  copper  powder,  which  is 
equal,  if  not  superior,  to  the  German  standard. 

(2)   Experimental  Part. 

A.  The  Preparation  of  Catalytic   Copper. — A   solution   of  chromous 
chloride  was  prepared  by  the  reduction  of  190  g.  of  commercial  sodium  di- 
chromate  by  means  of  an  excess  of  pure  zinc  (600  g.)  in  the  presence  of 
1250  cc.  of  concentrated  hydrochloric  acid.     The  acid  was  added  in  three 
portions.     The  reaction  was  vigorous,  generating  much  heat  with  the  evolu- 
tion of  much  steam,  acid  and  hydrogen.      The  color  changed  first  to  a 
green  and  finally  to  a  light  blue.     When  the  reaction  had  subsided  and  the 
reduction  was  complete,  the  mixture  was  freed  from  zinc  by  filtration 
through  glass  wool.     The  chromous  chloride  was  protected  from  oxida- 
tion by  a  rapid  current  of  carbon  dioxide.     The  solution  was  now  rapidly 
cooled. 

A  solution  of  120  g.  of  crystallized  copper  sulfate  in  700  cc.  of  water  was 
prepared  and,  shaken  well,  cooled  in  a  freezing  bath  until  it  had  become 
filled  with  a  mass  of  ice  crystals.  The  mixture  was  now  poured  into 
the  chromous  chloride  with  proper  stirring.  The  reduction  is  quantita- 
tive and  instantaneous.  The  precipitated  copper  was  washed  by  decanta- 
tion  with  much  water,  then  with  absolute  alcohol,  then  transferred  to  a 
suction  filter  and  washed  with  benzene  and  finally  with  a  solution  of 
vaseline  in  benzene.  The  vaseline  prevents  oxidation  by  the  air  and 
makes  the  preparation  quite  stable.  The  yield  is  theoretical. 

The  copper  thus  prepared  forms  a  light  red  powder,  which  is  exceed- 
ingly finely  divided,  without  any  metallic  luster.  Rubbed  between  the 
fingers,  it  remains  on  the  skin  like  flour. 

For  catalytic  purposes  in  the  phenylation  of  aromatic  amines  the  copper 
may  be  used  alone  or  it  may  be  mixed  with  a  small  amount  of  potassium 
iodide  as  recommended  by  Irma  Goldberg.1 

B.  T.he  Preparation  of  the  Three  Nitro-triphenylamines. — For  the  prep- 
aration of  a  nitro-triphenylamine  by  phenylation,  we  can  start  directly  from 
the  respective  nitraniline.     First  one  phenyl  group  is  introduced  and  the 
nitro-diphenylamine  formed  reacts  then  with  a  second  molecule  of  phenyl 
iodide.     In  this  manner  we  get  in  addition  to  unchanged  nitraniline  and 
nitro-diphenylamine,  the  nitro-triphenylamine  together  with  a  quantity 
of  tarry  by-products.     As  the  nitro-triphenylamine  has  no  basic  properties, 
its  isolation  and  purification  is  a  disagreeable  piece  of  work.     We  find 
that  the  tarry  products  are  only  formed  during  the  first  step  of  the  reaction, 
they  are  derivatives  of  the  nitraniline  and  not  of  the  nitro-di-  or  the  nitro- 
triphenylamines.     For  this  reason  it  is  better  to  make  first  in  one  way  or 

1  Ber.,  40,  4542  (1907). 


another  a  pure  nitro-diphenylamine  and  then  phenylate  this.     We  have 
then  but  to  isolate  the  nitro-triphenylamine  from  a  nitrobenzene  solution 
which  contains  only  a  very  small  amount  of  unchanged    nitro-diphenyl- 
amine, if  any,  no  nitraniline  and  no  tar. 
Nitro-triphenylammes.— 

H       H 


H       H 

Two  grams  of  pure  ^-nitro-diphenylamine,  5  cc.  of  phenyl  iodide,  o .  7  g. 
of  potassium  carbonate,  about  0.1-0.2  g.  of  copper  powder  mixed  with 
a  little  potassium  iodide,  were  boiled  together  with  10  cc.  of  nitrobenzene 
under  a  reflux  condenser  for  30  hours  on  a  sand  bath.  The  excess  of 
phenyl  iodide  and  of  nitrobenzene  was  removed  by  steam  distillation. 
The  mixture  remaining  was  extracted  with  ether  and  the  extract  filtered. 
After  due  removal  of  the  ether  and  after  cooling,  the  residue  crystallized. 
Any  unchanged  p-nitro-diphenylamine  was  completely  removed  by  treat- 
ment with  warm  concentrated  hydrochloric  acid.  The  ^-nitro-triphenyl- 
amine was  recrystallized  from  50%  alcohol.  The  pure  substance  melted 
at  140°  and  when  mixed  with  the  product  of  direct  nitration  of  triphenyl- 
amine,1  no  depression  was  observed.  Thus,  the  direct  nitration  gives 
the  para  product.  The  statement  that  decomposition  occurs  at  the  melting 
point  is  incorrect.  The  crude  yield  (m.  p.  133°)  was  94%  of  the  theo- 
retical. 

Pure  w-nitro-diphenylamine  (2  g.)  was  heated  at  boiling  for  30  hours, 
together  with  5  cc.  of  phenyl  iodide,  o .  7  g.  of  potassium  carbonate,  about 
0.2  g.  of  copper  mixed  with  a  little  potassium  iodide,  and  10  cc.  of  nitro- 
benzene. The  mixture  acquired  a  lighter  color  as  the  reaction  went  on. 
The  excess  of  phenyl  iodide  and  nitrobenzene  was  removed  by  a  steam 
distillation.  After  treatment  with  concentrated  hydrochloric  acid,  the 
crude  light  yellow  residue  was  recrystallized  from  dilute  alcohol  and  also 
from  methyl  alcohol.  The  crude  product  melted  at  75-76°  and  the  pure 
product  at  78°.  Recrystallization  from  acetic  acid  did  not  change  the 
melting  point.  The  crude  yield  was  about  95%  and  only  a  few  per  cent, 
were  lost  during  further  purification. 

Subst.  0.1120;  CC>2,  0.3044;  H2O,  0.0500. 
0.0674;  CO2,  0.1837;  H2O,  0.0307. 
0-2833;  24  .9  cc.  dry  N2  at  22°  and  726  mm. 

Calc.  for  Ci8H14O2N2:  C,  74 .46;  H,  4  .86;  N,  9  .66.    Found:  C,  74  . 14,  74  .36;  H,  4 .99, 
5  .10;  N,  9.72. 

1  M.  p.  139-140°  according  to  Herz. 


The  w-nitro-triphenylamine  is  lemon-yellow  similar  to  w-nitraniline ; 
both  differ  from  the  w-nitro-diphenylamine,  which  is  brick-red.  It  is  very 
soluble  in  nitrobenzene,  benzene,  ether,  and  ethyl  acetate;  moderately 
soluble  in  alcohol,  insoluble  in  water  and  acids.  However,  it  is  quite  solu- 
ble in  glacial  acetic  acid  and  in  concentrated  sulfuric  acid.  The  latter 
solution  at  first  is  colorless,  but  acquires  a  blue  coloration  in  a  few  seconds. 

Pure  0-nitro-diphenylamine  (2  g.)  was  phenylated  in  the  same  manner 
as  the  corresponding  w-derivative.  Here  also  the  reaction  is  quantita- 
tive. The  crude  product,  2.6  g.,  melted  at  96°.  After  several  recrys- 
tallizations  from  alcohol,  the  melting  point  rose  to  98°  and  there  remained 
constant.  Recrystallizations  from  ethyl  alcohol  did  not  change  the 
melting  point.  The  crude  yield  was  95%  of  the  theoretical. 
Subst.  0.1343;  CO2,  0.3656;  H2O,  0.0609. 

0.2180;  18.5  cc.  dry  N2  at  21°  and  734  mm.  (CuO). 
0.1051;  9.35  cc.  dry  N  at  21°  and  725  .5  mm.  (PbCrO4). 

Calc.  for  Ci8H]4O2N2:  C,  74.46;  H,  4.86;  N,  9.66.     Found:  C,  74-27;  H,  5  07; 
N,  9.52,  9.87. 

The  o-nitro-triphenylamine  is  yellow-orange  in  color.  In  large  crystals 
it  is  orange-brown.  Its  properties  are  very  similar  to  those  of  the  already 
described  para  and  meta  derivatives. 


II. 

THE  OXIDATION  OF  DIAMINOPHENOLS.* 
Theoretical  Part. 

That  diaminophenols  on  oxidation  give  red  solutions  is  known  to  all 
who  have  worked  with  these  substances.  F.  Kehrmann  and  H.  Prager1 
succeeded  in  isolating  some  of  these  oxidation  products  and  recognized 
them  as  salts  of  holoquinoid2  aminoquinonimines.  Some  years  later, 
Jean  Piccard3  re-investigated  these  compounds ;  by  titration  and  by  reduc- 
tion to  the  original  leucobase  he  confirmed  the  formulas  given  by  Kehr- 
mann and  Prager.  On  the  other  hand,  he  compared  the  absorption  spectra 
with  those  of  the  meriquinoid  salts,4  selecting  such  representatives  as  the 

*  Published  by  Jean  F.  Piccard  and  Louis  M.  Larseninthe  Journal  of  the  American 
Chemical  Society,  40,  1079-1092  (1918). 

1  Ber.,  39,  3438  (1906). 

2  Holoquinoid  is  applied  to  those  aromatic  compounds  which  possess  the  quinoid 
structure.     Quinone,  O  =  C6H4  =  O,  is  a  common  example.      Meriquinoid  is  applied 
to  those  quinonimine  salts,  whose  Ce  rings  are  (as  in  quinhydrone)  partly  quinoid  and 
partly  hydroquinoid.     Red  of  Wurster  and  magenta,  shown  above,  are  examples  of 
this  class.     They  have  always  a  very  pronounced  color  and  are  considered  as  the 
mother  substances  of  most  of   the   dyes.      (Willstatter  and    Piccard,  Ber.  41,   1465 
(1908)). 

3  Ber.,  42,  4339  (1909). 

4  A  part  of  this  work  was  done  by  Dr.  Piccard  in  the  Chemical  Laboratory  of  the 
Royal  Academy  of  Sciences  in  Munich  in  1912  but  has  not  previously  been  published. 


8 

Red  of  Wurster  (intermolecular  meriquinoid)  and  magenta  (intramolec- 
ular   meriquinoid). 

OH O  N(CH8)2 N(CH3)2Br        NH2. . .  .NH2O.  . .  .NH2 


OH O  NH2 NH2Ce 

Quinhydrone.  Red  of  Wurster. 

He  found  that  the  new  class  of  substances,  although  highly  colored  when 
compared  with  the  colorless  quinonimine  salts,  are,  however,  far  from  attain- 
ing the  color  brilliancy  and  intensity  of  the  true  meriquinoid  salts.  The 
latter  possess  characteristic  absorption  bands,  while  the  former  show  only 
a  general  absorption  in  the  violet  region  of  the  spectrum. 

Later,  from  the  work  of  F.  Kehrmann  and  St.  Micewicz1  and  of  Piccard2 
it  became  known  that  the  substitution  of  a  phenyl-immonium  group  for  the 
dimethyl-immonium  group  produces  in  the  case  of  the  simple  holoquinoid 
salts  a  great  lowering3  of  color,  while  in  the  meriquinoid  salts  only  a  very 
slight  change  is  produced.  Thus  tetramethylphenylendiamine  (CH3)2-N 
C6H4-N(CH3)2  gives  blue  meriquinoid  and  colorless  holoquinoid  salts,  while 
phenyldimethylphenylendiamine  (CHs^N-CeH^NHCeHs  and  diphenyl- 
phenylendiamine  CeHsNH-CeH^-NHCeHs  whose  meriquinoid  salts  are  also 
blue,  gives  red  holoquinoid  salts. 

These  interesting  relations  were  not  at  all  expected.  We  decided  to 
investigate  the  aminoquinonimine  salts  similarly  and  their  preparation 
is  the  object  of  our  present  work.  New  quinoid  salts  were  prepared  from 
2,4-diaminophenol  (I),  2-dimethylamino-4-aminophenol  (II),  and  2-phenyl- 
amino-4-aminophenol  (III).  We  find  that  in  this  class  of  substances  the 
usual  rule  holds,  e.  g.,  a  phenylamine  group  has  approximately  the  same 
effect  as  the  dimethylamine  group. 
O 


N(CH»),  ff      i)—  NHC6HS 


NH.HC1  NH.HC1 

Dimethylaminoquinonimine  salts  give  violet-red  solutions  and  phenyl- 
aminoquinonimine  salts  have  the  same  color. 

1  Ber.,  45,  2651  (1912). 

2  Ibid.,  46,  1850  (1913)- 

3  We  call  yellow  the  highest  color,  from  which  we  go  through  orange,  red,  violet 
and  blue  to  green,  which  is  then  the  lowest  color. 


Kehrmann  and  Prager1  oxidized  the  2,4-diaminophenol  (I)  as  well  as  a 
number  of  its  homologs,  (diamino-0-cresol,  diamino-w-cresol,  diamino- 
thymol)  and  isolated  holoquinoid  salts  either  as  nitrates  or  picrates,  or  as 
bichromates.  From  the  last  base  they  prepared  a  chloride,  a  double  salt 
with  mercury  chloride,  and  an  oxalate;  but  these  were  neither  analyzed 
nor  studied  further.  Since  the  analyzed  salts  prepared  by  Kehrmann  and 
Prager  are  unsuitable  for  titration,  Piccard2  isolated  and  titrated  thequinoid 
hydrochloride  of  diamino-o-cresol.  Its  constitution  was  definitely  shown 
to  be  holoquinoid. 

Since  the  simplest  of  the  substances  under  investigation,  e.  g.,  the  amino- 
quinonimine  has  been  known  only  as  the  picrate  and  the  bichromate,  both 
unsuitable  for  titration,  we  sought  the  salt  of  a  colorless  monobasic  acid3 
which  can  be  easily  titrated.  After  several  attempts  we  succeeded  in 
isolating  and  studying  the  properties  of  the  rather  unstable  and  easily 
soluble  hydrochloride. 

We  then  turned  our  attention  to  the  oxidation  of  the  corresponding 
dimethyldiamino — (II)  and  the  phenyldiamino — (III)  phenols,  so  that  a 
comparison  of  the  colors  of  the  oxidation  products  could  be  made,  this 
being  the  primary  object  of  this  paper. 

OH  OH  OH 

N(CH,)>  ,//\-NHC6H5 

\/ 

(I).  NH2  (II).  NH2  (III).  NH2 

NHC6H6  OH 

NH2— f     \— NH2 

V 

(IV).  NH2  (V).  NH2 

The  desired  dimethyldiaminophenol ,(H)  was  already  known.4  The  known 
phenyldiaminophenol5  (IV)  does  not  possess  the  desired  constitution. 
Therefore  we  tried  the  preparation  of  the  2-phenylamino-4-aminophenol 

cm). 

Gattermann6  has  shown  that  when  an  aromatic  nitro-compound  is  re- 
duced electrolytically  in  strong  sulfuric  acid,  a  ^-aminophenol  is  produced. 
Thus  from  nitrobenzene  he  prepared  the  ^-aminophenol,  from  m-nitraniline 

1  Ber.,  39,  3438  (1906). 

2  Ibid.,  42,  4339  ^1909). 

3  The  salts  of  hydrochloric  and  perchloric  acids  are  desirable  because  these  acids 
are  themselves  colorless  and  do  not,  as  do  nitric,  chromic,  sulfuric,  and  picric  acids, 
interfere  with  the  titration. 

4  L.  Gattermann,  Ber.,  27,  1932  (1894). 
6  L.  Kohler,  Ibid.,  21,  910  (1888). 

6  Ber  ,  26,  1847  (1893). 


10 

the  2,4-diaminophenol  (I),  and  from  w-nitrodimethylaniline  the  2-di- 
methylamino-4-aminophenol  (II) . 

We  now  applied  the  reduction,  introduced  by  Gattermann,  to  the  m- 
nitrodiphenylamine,  (w-nitrophenylaniline).  For  determining  whether 
or  not  the  phenyldiaminophenol  was  formed  and  for  following  the  course 
of  the  reaction  the  same  test  was  here  used  which  was  employed  in  detecting 
the  presence  of  the  diaminophenol  and  the  dimethyldiaminophenol  during 
their  preparation.  A  test  portion  (o.  i  cc.)  of  the  reaction  mixture  was  re- 
moved, diluted  with  5  cc.  water,  filtered  from  any  unchanged  nitro-com- 
pound  and  sulfur  (formed  from  the  reduction  of  some  of  the  acid),  and  then 
oxidized  with  a  dilute  solution  of  ferric  chloride.  The  formation  of  a  red 
solution  in  the  case  of  the  reduction  of  the  w-nitraniline  showed  that  the 
2,4-diaminophenol  was  formed;  similarly  in  the  case  of  the  w-nitrodimethyl- 
aniline a  violet-red  solution  was  formed.  In  the  case  of  the  reduction  of 
the  w-nitrodiphenylamine,  a  violet-red  coloration  was  produced.  The 
isolation  of  the  reduction  product  is  described  later.  Its  properties  and 
analysis  together  with  the  manner  of  preparation  show  that  it  is  indeed  the 
desired  2-phenylamino-4-aminophenol  (III). 

On  oxidation  the  two  phenyl-diaminophenols  gave  similar  violet-red  solu- 
tions. The  isolation  of  the  oxidation  product  of  the  phenyldiaminophenol 
(III)  as  the  hydrochloride,  the  nitrate,  and  the  perchlorate  was  unsuccess- 
fully attempted.  These  salts  were  found  to  be  too  soluble  and  also  un- 
stable in  the  concentrated  solutions,  rapidly  forming  condensation  products. 
We  prepared  the  picrate  for  analysis.  For  observations  on  the  color  of 
the  oxidation  product  freshly  prepared  dilute  solutions  of  the  hydrochloride, 
which  need  not  be  isolated  in  the  solid  condition,  were  employed. 

The  oxidation  of  leucobase  may  give  rise  to  holoquinoid,  meriquinoid, 
or  to  condensation  products.  Usually,  it  is  not  necessary  to  isolate  the 
product  in  order  to  determine  whether  or  not  condensation  has  taken  place. 
A  suitable  amount  of  the  substance  in  excess  is  oxidized  by  a  standard  solu- 
tion of  an  oxidizing  agent,  and  the  resulting  colored  solution  is  titrated 
to  the  disappearance  of  color  by  a  standard  solution  of  a  reducing  agent. 
If  equivalent  amounts  of  the  reagents  are  required,  no  condensation  has 
taken  place ;  but  if  less  than  an  equivalent  amount  of  the  reducing  reagent 
is  needed,  a  condensation  or  a  substitution1  has  taken  place.  On  oxidation 

of  HO — \        >> — NH2  2  molecules  of  the  leucobase  require  2  atoms  of 

O 

OH  i| 

(   \—  NH  —ill—  NH2 
oxygen.     After   condensation  to  I        I  (II  ,    for   instance, 

NH2  Y 

NH 
1  If  a  halogen  is  used  as  the  oxidizing  agent,  substitution  may  readily  take  place. 


11 

only  2  atoms  of  hydrogen  would  be  required  for  reduction.  But  when  the 
right  conditions  (temperature,  concentration,  oxidizing  agent,  etc.)  were 
chosen,  experiment  showed  that  4  atoms  of  hydrogen  were  required  for 
decolorization,  showing  that  no  appreciable  condensation  has  taken  place.1 
This  method  was  applied  to  each  of  the  diaminophenols  to  ascertain  whether 
or  not  a  condensation  takes  place  during  the  oxidation.  In  each  case  it 
was  found  that  the  first  product  of  oxidation  is  not  one  of  condensation, 
but  that  condensation  may  take  place  afterwards,  less  readily  when  the 
solution  is  made  more  dilute  and  when  it  is  cooled. 

Two  methods  are  used  to  determine  whether  the  product  of  oxidation  is 
holoquinoid  or  meriquinoid.  One  method  consists  in  oxidizing  equal 
amounts  of  the  leucobase,  whose  molecular  weight  and  number  of  hydro- 
quinoid  nuclei  are  known,  with  different  amounts  of  a  standard  solution 
of  an  oxidizing  agent  until  the  maximum  intensity  of  the  color  is  reached. 
If  one  atom  of  oxygen  for  every  hydroquinoid  nucleus  is  needed  for  this 
oxidation,  the  product  is  holoquinoid,  but  if  less  than  this  amount  is  needed 
(usually  1/2  or  l/8),  the  product  is  meriquinoid.  The  other  method,  ap- 
plicable only  when  the  oxidation  product  has  been  isolated,  consists  in  the 
titration  of  a  known  amount  of  the  latter,  whole  molecular  weight  must 
be  known,  to  the  disappearance  of  color  with  a  standard  solution  of  a  re- 
ducing agent.  From  these  data  the  constitution  of  the  substance  is  readily 
determined. 

Both  methods,  applied  to  the  aminophenols  (I  to  V  inclusive),  showed 
that  these  substances  form  holoquinoid,  not  meriquinoid,  salts  on  oxidation. 

The  introduction  of  one  auxochromic  amino  group  into  quinonimine  is 
accompanied  by  a  change  of  the  color  of  the  solution  from  almost  colorless 
to  red.  The  addition  of  strong  acid  to  this  red  solution  changes  it  to  a 
pale  yellow,  due  to  salt  formation  with  the  auxochrome  group.  The  intro- 
duction of  one  more  amino  group  into  the  quinonimine  is  accompanied  by 
a  change  of  the  color  from  red  to  blue:  the  2,6-diaminoquinonimine  hydro- 
O 


chloride  2  has  been  prepared  and  described  by  HeintzelJ 


NH2C1 

The  addition  of  strong  acid  changes  the  blue  solution  to  a  red,  one  of  the 
two  auxochrome  groups  being  neutralized  and  the  effect  produced  is  the 
same  as  if  that  group  were  entirely  eliminated. 

The  aminoquinonimine  salts,  as  a  class,  differ  considerably  from  the  tri- 

1  Not  too  concentrated  solutions  were  employed  here,  for  the  oxidation  is  followed 
by  condensation  reactions,  which  had  to  be  avoided  as  much  as  possible. 

2  Z.  Chem.,  1867,  342. 


12 

phenylmethane  dyes  in  that  they  are  much  less  brilliant  than  the  latter, 
and  also  in  that  they  lose  the  color  intensity  in  decreasing  thickness  of 
layers,  more  rapidly  than  do  the  latter;  a  0.004%  solution  of  the  dimethyl- 
aminoquinonimine  perchlorate  when  viewed  laterally  through  a  tube, 
1.5  cm.  in  diameter,  was  exactly  matched  by  a  0.001%  solution  of  triphenyl- 
methane  dyes  (made  by  mixing  10  cc.  of  a  0.001%  solution  of  crystal 
violet  with  100  cc.  of  rosaniline  acetate  of  the  same  strength),  but  when 
viewed  through  a  layer  of  20  cm.  the  quinonimine  solution  was  much  deeper 
in  color.  On  the  other  hand  through  a  layer  of  0.25  cm.  thickness  it  was 
lighter.  Through  the  spectroscope  the  triphenylmethane  dyes  at  the 
above  concentration  showed  very  pronounced  absorption  bands  through  a 
thickness  of  1.5  cm.,  whereas  the  quinonimine,  even  when  considerably 
more  concentrated,  showed  no  appreciable  absorption  bands  whatever. 

The  absorption  spectra  of  the  dimethylamino-  and  the  phenylamino- 
quinonimine  salts  show  only  general  absorption  in  the  green  and  the  green- 
blue  regions  of  the  spectrum.  The  former  are  characterized  by  a  slightly 
sharper  absorption  curve  and  are  thus  slightly  more  brilliant  than  the  latter. 
Also,  their  color,  with  decreasing  thickness  of  layers,  decreases  a  little  more 
slowly  than  that  of  the  latter  salts.  Even  the  2,6-diaminoquinonimine 
salts  have  no  sharp  bands  but  possess  general  absorption  with  a  wide  maxi- 
mum in  the  orange.  These  lose  their  intensity  like  the  salts  of  the  other 
quinonimines  (holoquinoid) . 

Although  we  are  unable  to  say  with  certainty  whether  the  structure  of 
these  compounds  is  para-  or  orthoquinoid,  still  we  are  led  to  believe  that 
the  former  (A)  is  correct.  The  following  gives  the  possible  formulas  for 
the  holoquinoid  phenylamino  derivative: 

00  00 

'C6H6 


NH2X  NH  ,       NH3X  NH2 

(A).  (B).  (C).  (D). 

Formula  C  is  impossible  for  the  special  case  of  the  dimethylamino  com- 
pound. Formulas  B  and  C  are  both  unlikely  for  all  cases  because  no  auxo- 
chrome  group1  is  present.  Formula  A  is  preferable  to  D  because  the  imino 
group  (  =  NH)  is  more  basic  than  the  phenylimino  group  (  =  NC6H6). 
Formula  A  has  also  become  accepted  for  the  dimethylamino  derivative, 
but  for  this  substance  no  definite  proof  has  yet  been  found  against  the  con- 
stitution D. 

The  solutions  of  our  compounds  could  also  involve  an  equilibrium  be- 
tween different  forms. 

1  The  group  ( — NRjX)  is  not  an  auxochrome  group. 


13 

Experimental  Part, 
i.  Oxidation  of  2,4-Diaminophenol  (I).    A.  Preparation  of  the  Quinoid 

o 


Hydrochloride,  [I  2. — The  diaminophenol  has  been  oxidized  with 


NH.HC1 

ferric  chloride  by  Kehrmann  and  Prager.1  They  prepared  the  hydrochlo- 
ride  by  shaking  the  reaction  mixture  with  solid  sodium  chloride,  but  they 
were  unable  to  separate  the  easily  soluble  hydrochloride  from  excess  of 
sodium  chloride.  Since  the  salts  prepared  and  analyzed  by  them  are 
unsuitable  for  titration,  we  tried  to  prepare  the  pure  hydrochloride. 

We  observed  that  the  hydrochloride  is  quite  unstable  in  concentrated 
solutions.  A  strong  aqueous  solution,  even  at  o°  changes  within  a  few 
seconds,  forming  brown  condensation  products.  Thus  it  becomes  abso- 
lutely necessary  in  its  isolation  to  avoid  washing  the  salt  with  pure  water. 
For  this  reason,  attempts  were  made  to  precipitate  the  salt  with  a  concen- 
trated solution  of  calcium  chloride,  the  latter  being  washed  out  with  abso- 
lute alcohol.  In  this  manner  we  obtained  an  excellent  yield,  but  on  igni- 
tion some  ash  remained. 

On  the  other  hand,  a  slight  excess  of  ferric  chloride  may  be  used  to  pre- 
cipitate the  salt  in  concentrated  solutions.  If  too  concentrated,  the  leu- 
cohydrochloride  precipitates  before  its  oxidation  becomes  complete.  The 
method  described  below  gave  us  a  preparation  whose  ash  was  negligible. 
We  sacrificed  the  yield  in  this  and  other  preparations  in  order  that  the 
products  might  be  obtained  directly  in  pure  condition. 

Four  g.  of  pure  recrystallized  2,4-diaminophenoldihydrochloride2  in 
50  cc.  water  at  o°  was  oxidized  by  20  cc.  of  a  4  N  ferric  chloride  solution 
(650  g.  sublimed  ferric  chloride  per  liter  of  solution)  cooled  to  o°.  The 
deep  red  solution  was  further  cooled  and  held  at  — 15°  for  15  minutes. 
The  formation  of  red  crystals  was  noted  after  a  few  moments  of  vigorous 
rubbing.  The  precipitate  was  collected  on  a  suction  filter,  washed  with 
cold  absolute  alcohol  ( — 20°)  and  with  absolute  ether.  By  keeping  the 
substance  covered  with  absolute  ether,  care  was  taken  to  prevent  air  cur- 
rents from  depositing  moisture  upon  the  substance.  The  presence  of  even 
small  amounts  of  water  causes  it  to  turn  brown  and  finally  black.  The 
preparation  was  dried  to  constant  weight  within  4  days,  over  sulfuric  acid 
and  soda-lime  in  vacuo.  The  yield  was  50%  of  the  theoretical. 

For  titration,  the  salt  was  dried  only  6  hours.  A  suitable  portion  was 
dissolved  rapidly  in  50  cc.  of  water,  acidified  with  10  cc.  of  oxygen-free 

1  Ber.,  39,  3437  (1906). 

2  L.  Gattermann,  Ibid.,  26,  1849  (1893). 


14 

normal  acid,  a  small  quantity  of  sodium  fluoride1  added,  and  titrated  im- 
mediately with  0.03  N  titanium  trichloride  in  an  atmosphere  of  carbon 
dioxide.  At  the  end,  the  reduction  was  hastened  by  warming  the  solution 
to  40°.  The  endpoint  was  partly  masked  by  the  presence  of  a  light  brown 
coloration.  Fair  results  were,  nevertheless,  obtained. 

Subst.,  0.1484;  CO2,  0.2481;  H2O,  0.0622.  Subst.,  0.1504;  23.25  cc.  dry  N2  at 
18°  and  733  mm.  Subst.,  0.1906;  0.1721  AgCl.  Subst.,  0.0607,  0.0614,  0.0454;  25.70, 
25.35,  19.20  cc.  0.03  N  TiCl3. 

Calc.  for  C6H7ON2C1:  C,  45.42;  H,  4.45;  N,  17.67;  Cl,  22.36;  H  equiv.,  79.25. 

Found:  C,  45.61;  H,  4.69;  N,  17.50;  Cl,  22.34;  H  equiv.,  78.7,  80.7,  78.8. 

This  salt  is  shown  by  the  titration  to  be  holoquinoid.  Condensation 
products  and  meriquinoid  salts  of  the  same  composition  would  require  less 
hydrogen  for  reduction. 

In  reflected  light  the  preparation  shows  some  green  surface  color  and  when 
rubbed  to  thin  layers  on  a  watch  glass,  the  salt  appears  violet-red. 

This  salt  crystallizes  in  2  forms  :  a  light  one,  consisting  of  light  red 
needles,  without  any  complementary  surface  color,  and  a  dark  one,  consis- 
ting of  plates,  with  a  green  surface  color.  The  light  form  soon  changes  into 
the  stable  dark  modification.  This  occurs  rapidly  when  a  portion  of  the 
mother  liquor,  in  which  the  light  red  needles  are  suspended,  is  seeded  with 
a  little  of  the  dark  modification.  The  needles  are  observed,  under  the 
microscope,  to  go  back  into  solution  and  the  dark  plates,  being  less  soluble, 
precipitate  out.  We  have  not  been  able  to  isolate  the  light  modification 
of  the  chloride.  But  in  the  case  of  the  perchlorate  and  the  nitrate,  de- 
scribed below,  the  salts  are  light  red  without  any  complimentary  surface 
color.  These  are  then  the  light  modifications.  This  curious  phenomenon 
of  2  isomeric  forms  has  been  observed  before  in  the  preparation  of  other 
quinonimines.2 

The  earlier  suggestion  that  the  light  and  the  dark  forms  possess  the  para 
and  the  ortho  quinoid  formulas  has  now  been  abandoned.  They  form 
identical  solutions  and  are  believed  to  be  different  states  of  aggregation. 

When  kept  dry  the  salt  is  stable  for  a  week  or  more.  Acid  solutions  are 
far  more  stable  than  neutral  ones.  In  dilute  aqueous  solution  it  is  stable 
for  several  hours,  but  in  concentrated  solutions  a  rapid  change  occurs. 
This  change  is  not  due  to  hydrolysis  but  to  a  condensation  reaction,  for  its 
velocity  is  markedly  dependent  upon  concentration.3  If  we  place  equal 
quantities  (o.oi  g.)  of  the  salt  in  2  dishes,  rub  one  portion  a  few  seconds 
with  0.5  cc.  of  water,  and  then  throw  both  dishes,  with  stirring,  into  a 

1  J.  Piccard,  Ber.,  42,  4343  (1909). 

2  Ibid.,  42,  4338  (1909). 

3  The  velocity  of  multimolecular  reactions  is  dependent  upon  the  concentration, 
whereas  the  rate  of  hydrolysis  is  mono-molecular  with  respect  to  the  substance  and 
practically  independent  of  concentration,  if  the  latter  is  not  too  great. 


15 

liter  of  water  each,  the  first  forms  a  dark  brown  solution,  while  the  second 
shows  a  brilliant  wine-red  coloration  which  only  after  several  hours  becomes 
brown. 

The  hydrochloride  is  readily  soluble  in  water,  soluble  in  alcohol  but  in- 
soluble in  acetone.  Its  solutions  have  a  red  color  like  that  of  ferric  thio- 
cyanate.  On  the  addition  of  cone,  sulfuric  acid  the  red  of  the  amino- 
quinonimine  changes  to  a  pale  yellow,  due  to  the  absorption  of  a  second 
acid  equivalent  by  the  auxochrome  group.  The  solution  on  dilution  be- 
comes red  again. 

The  spectrum  shows  general  absorption  in  the  violet  region. 

B.  Preparation  of  the  Quinoid  Perchlorate  and  Nitrate. — Since  the  per- 
chlorate  of  the  dimethyl  derivative,  described  below,  was  found  by  titra- 
tion  to  be  of  high  purity,  we  attempted  the  preparation  of  a  perchlorate 
of  aminoquinonimine  in  analogous  manner.  Beautiful,  glistening  light  red 
needles  were  isolated,  which  when  heated  exploded  violently,  a  common 
property  of  organic  perchlorates.  Analysis  showed,  however,  that  the 
preparation  was  not  pure.  Its  ash  was  approximately  0.7%  and  chlorine 
determinations  gave  16.65%  and  16.60%,  respectively.  The  value  cal- 
culated in  the  pure  perchlorate  for  chlorine  is  15.93%. 

As  the  solubility  of  the  chloride  is  not  much  greater  than  that  of  the 
perchlorate,  the  preparation  of  the  latter  was  attempted  by  using  ferric 
nitrate,  instead  of  ferric  chloride.  The  salt  obtained  was,  however,  not  a 
perchlorate  but  a  nitrate.  Further  work  on  the  perchlorate  was  dropped 
at  this  point,  as  this  salt  is  not  essential  for  our  observations. 

The  yield  of  the  nitrate  was  increased  by  the  addition  of  a  concentrated 
solution  of  sodium  nitrate.  The  preparation  obtained  according  to  the 
following  procedure,  left  no  ash  on  ignition : 

Two  g.  of  pure  recrystallized  2,4-diaminophenoldihydrochloride  in  40 
cc.  water  at  o°  was  oxidized  by  20  cc.  of  2  N  ferric  nitrate  solution  cooled 
to  o°.  Crystallization  of  the  nitrate  began  almost  immediately.  To  the 
mixture,  cooled  to  — 15°,  was  added  20  cc.  of  a  cold  saturated  solution  of 
sodium  nitrate.  After  15  minutes,  the  precipitate  was  collected  on  a  suc- 
tion filter  and  rapidly  washed  with  a  little  cold  absolute  alcohol  ( — 20°), 
a  little  cold  water  (o°),  considerable  cold  absolute  alcohol  and  much 
dry  ether.  The  preparation  was  dried  in  vacuo,  requiring  4  days  to  attain 
constant  weight.  The  yield  was  about  50%  of  the  theoretical. 

Subst.,  0.1505;  2955  cc.  dry  N2  at  15°  and  735  mm. 
Calc.  for  C6H7O4N3:  N,  22.71.     Found:  22.53. 

The  nitrate  is  easily  soluble  in  water,  somewhat  soluble  in  alcohol  and 
acetone,  but  insoluble  in  chloroform.  It  is  not  as  readily  blackened  by 
moisture  as  is  the  chloride.  Its  properties  are  similar  to  those  of  the  chlo- 
ride. Only  one  modification  was  observed :  long,  bright  red  needles. 


16 

II.  Oxidation  of  the  2-Dimethylamine-4-aminophenol.    A.  Preparation 

o 


of   the   Quinoid  Perchlorate,  I!     it  3  \ — A  solution  of  5  g.  of  pure 

ii 

NH.HC104 

recrystallized  2-dimethylamino-4-aminophenol-di-hydrochloride1  in  50 
cc.  water  at  o°  was  oxidized  by  25  cc.  of  a  4  N  solution  of  ferric  chloride  at 
o°.  An  intense  violet-red  coloration  was  produced.  A  solution  of  pure 
sodium  perchlorate  (30  cc.),  saturated  at  20°,  was  added  to  the  reaction 
mixture.  After  a  few  moments,  crystallization  began.  After  being  cooled 
at  — 20°  for  half  an  hour,  the  perchlorate  was  collected  and  washed  suc- 
cessively with  a  saturated  solution  of  sodium  perchlorate  at  — 20°,  cold 
absolute  alcohol,  a  few  drops  of  ice-cold  water,  more  cold  absolute  alcohol, 
and  alcohol-ether  mixture,  and  finally  with  much  dry  ether.  The  prepara- 
tion was  immediately  placed  in  a  desiccator  and  dried  in  the  usual  manner. 
Constant  weight  was  obtained  almost  at  once.  The  yield  was  25-30% 
of  the  theoretical. 

The  chlorine  determination  was  made  by  the  following  rapid  and  con- 
venient method,  introduced  by  K.  Hofmann:2  A  suitable  quantity  of  the 
material  is  intimately  mixed  in  a  platinum  crucible  with  pure  sodium 
carbonate  (8  g.)  and  covered  with  more  carbonate.  To  avoid  loss  of  ma- 
terial resulting  from  too  vigorous  a  reaction,  we  heated  the  top  layers 
first.  The  organic  matter  is  completely  oxidized  leaving  an  excess  of 
sodium  perchlorate,  and  the  operation  is  complete  only  after  this  has  been 
converted  into  the  chloride.  The  cooled  mass  is  dissolved  in  water,  neu- 
tralized with  dil.  nitric  acid,  and  the  chlorine  precipitated  by  silver  nitrate. 
For  titration  a  suitable  portion  of  the  perchlorate  was  reduced  with  0.03 
N  titanium  trichloride,  great  care  being  taken  not  to  overstep  the  end- 
point.  The  reduction  was  rather  slow  but  complete.  The  solution  showed 
no  brown  coloration  whatever  at  the  end-point.  The  values  obtained 
show  that  this  substance  is  holoquinoid,  and  also  that  it  is  very  pure. 

Subst.,  0.1952,  0.2070;  CO2,  0.2742,  0.2891;  H2O,  0.0784,  0.0834.  Subst.,  0.2169, 
0.3084;  21.15  cc.  dry  N2  at  22°  and  751  mm.  30.30  cc.  dry  N2  at  24.5°  and  748  mm. 
Subst.,  0.2200,  0.2680;  AgCl,  0.1273,  0.1528.  Subst.,  0.1107,  0.1122;  29.33,  29-75  cc. 
0.03  N  TiCl3. 

Calc.  for  C8HiiO5N2Cl:  C,  38.31;  H,  4.42;  N,  11.18;  Cl,  14.15;  H  equiv.,  125.3. 
Found:  C,  38.32,  38.10;  H,  4.49,  4.51;  N,  11.16,  11.10;  Cl,  14.31,  H-0?;  H  equiv., 
125.8,  125.7. 

The  perchlorate  crystallizes  in  light  red  needles.     Its  solutions  have  a 
very  beautiful  violet-red  color.     Dilute  solutions  were  found  stable  for 

1  L.  Gattermann,  Ber.,  27,  1932  (1894). 

2  K.  Hofmann,  A.  Metzler  and  K.  Hobold,  Ibid.,  43,  1081  (1910). 


17 

several  days.  Condensation  products  are  formed  here  too,  but  less  readily 
than  from  the  simple  amino  derivative  (described  above).  The  salt  is 
readily  soluble  in  water,  quite  soluble  in  alcohol,  acetone,  glacial  acetic  acid 
but  insoluble  in  chloroform.  Like  the  salts  of  the  previous  aminoquinon- 
imine,  its  color  is  not  changed  by  strong  acids  except  concentrated  sulfuric 
acid,  in  which  it  dissolves  to  a  pale  yellow  solution.  The  latter  solution  on 
dilution  again  becomes  violet-red. 

The  light  red  crystals  were  observed  to  change  slowly  on  standing,  be- 
coming darker.  Analysis  showed  that  the  chlorine  content  remained 
unchanged. 

The  absorption  curve  of  the  perchlorate  is  quite  flat  with  a  wide  maximum 
in  the  green. 

B.  Preparation  of  the  Picrate. — The  picrates  of  the  quinonimines  are 
insoluble  and  can  be  prepared  readily  with  a  good  yield.  But  due  to 
hydrolysis  and  often  to  precipitation  of  picric  acid  in  the  acid  solution,  they 
are  difficult  to  obtain  in  pure  condition. 

A  solution  of  one  g.  of  2-dimethylamino-4-aminophenoldihydrochloride 
in  25  cc.  water  at  o°  was  oxidized  by  5  cc.  of  a  cold  4  N  solution  of  ferric 
chloride.  The  resulting  violet-red  solution  was  added  slowly  to  a  cold 
solution  of  2  g.  picric  acid  in  350  cc.  water.  Crystallization  took  place  im- 
mediately. The  mixture  was  cooled,  and  the  dark  brown  crystals  were 
collected,  washed  with  25  cc.  of  cold  dil.  picric  acid  solution  and  about  20 
cc.  of  ice  cold  water.  The  preparation  was  dried  in  vacua  to  constant 
weight.  The  yield  amounted  to  90%  of  the  theoretical. 

Subst.,  0.2256;  CO2,  0.3632;  H2O,  0.0718.    Subst.,  0.1619;  26.75  cc.  dry  N2  at  21° 
and  736  mm. 

Calc.  for  Ci4H13O8N6:  C,  44-33;  H,  3.45;  N,  18.47.     Found:  C,  43-92;  H,  3.56;  N, 
18.60. 

The  picrate  dissolves  with  a  red  color,  readily  in  alcohol  and  acetone, 
sparingly  in  chloroform  and  water.  When  the  salt  is  warmed  with  water, 
hydrolysis  with  subsequent  decomposition  occurs.  It  dissolves  easily  in 
acids  giving  violet-red  solutions.  It  crystallizes  in  clusters  of  long  needles. 

III.  Oxidation  of  3-Phenylamino-6-aminophenol. — This  phenol  (IV) 
has  been  isolated  and  described  by  Kohler.1  On  oxidation  with  ferric 
chloride  it  gives  solutions  having  the  same  violet-red  color  as  those  pre- 
pared from  the  preceding  dimethyldiaminophenol.  By  oxidation  and  then 
by  reduction  we  have  been  able  to  show  that  no  appreciable  condensation 
takes  place,  for  equivalent  amounts  of  standard  solutions  are  used  for  both 
operations. 

Salts  of  this  quinonimine  were  not  isolated,  because  we  are  now  able  to 
prepare  the  desired  phenol  (III)  and  from  it  the  quinonimine  picrate. 
1  Ber.,  21,  910  (1888). 


18 
IV.  Preparation  of  2-Phenylamino-4-aminophenol  Dihydrochloride, 

OH 

{  \— NHC6H6.HC1 

I       1  . — Ten  g.  of  w-nitrodiphenylamme1  prepared  by  the 

NH2.HC1 

phenylation2  of  w-nitraniline  were  dissolved  with  gentle  warming  in  85 
cc.  of  cone,  sulfuric  acid  and  reduced  electrolytically.3  The  average 
amperage  and  voltage  for  the  20-hour  run  were  1.5  and  6.5,  respectively. 
Each  electrode  was  of  15  sq.  cm.  surface.  From  time  to  time,  test  portions 
were  removed,  diluted,  filtered  from  any  unchanged  nitro-compound,  and 
oxidized  by  ferric  chloride.  During  the  reduction,  the  nitro-compound 
gradually  disappeared  and  the  violet-red  coloration,  formed  in  the  test 
portion  by  oxidation  with  ferric  chloride,  became  correspondingly  more 
intense.  After  but  little  of  the  unchanged  nitro-compound  was  left,  the 
acid  solution  was  filtered  and  then  diluted  with  500  g.  of  crushed  ice.  A 
red  precipitate  (2  g.)  formed,  from  which  a  gram  of  unchanged  w-nitro- 
diphenylamine  was  recovered.  After  filtration,  the  acid  solution  was 
neutralized  by  sodium  carbonate  and  some  sodium  sulfite,  the  operation 
being  completed  with  bicarbonate.  The  aminophenol  was  repeatedly 
extracted  from  the  neutral  solution  with  ether.  The  ether  solution  was 
clarified  with  anhydrous  sodium  sulfate,  filtered  and  shaken  well  with  an 
excess  of  dil.  hydrochloric  acid.  The  resulting  acid  solution  was  filtered 
and  evaporated  to  dryness  under  reduced  pressure  in  the  absence  of  air. 
Crystals,  slightly  pink  from  oxidation,  appeared  toward  the  end.  The 
product  was  powdered  and  dried  in  vacua.  The  salt  is  very  hygroscopic 
and  when  exposed  to  the  air  is  rapidly  oxidized,  finally  forming  a  dark 
brown  product.  The  yield  amounted  to  7.8  g.  Constant  weight  was  not 
attained  within  2  weeks  due  to  a  loss  of  hydrochloric  acid  and  also  to 
gradual  oxidation.  It  then  gave  the  following  analysis : 

Subst.,  0.1600;  CO2,  0.3130;  H2O,  0.0776.  Subst.,  0.1626;  15.20  cc.  dry  N2  at  20° 
and  724  mm.  0.1643;  AgCl,  0.1605. 

Calc.  for  Ci2Hi2ON2.2HCl:  C,  52.75;  H,  5.16;  N,  10.26;  Cl,  25.97.  Found:  C, 
53.24;  H,  5.41;  N,  10.57;  Cl,  24.17. 

The  salt  is  very  soluble  in  water,  moderately  soluble  in  alcohol  and 
difficultly  in  glacial  acetic  acid.  On  being  heated  it  turns  brown.  An 
aqueous  solution  forms  on  standing  a  dark  amorphous  precipitate,  insoluble 
in  dilute  acids.  Oxidized  with  a  limited  amount  of  bromine,  phenylamino- 
quinonimine  is  produced;  an  excess  of  bromine  precipitates  a  yellow  sub- 

1 1.  Goldberg,  Ber.,  40,  4545  (1907). 

2  In  our  first  paper  (J.  Am.  Chem.  Soc.,  39, 2006  (1917))  we  indicated  in  Footnote  3, 
page  2006  by  mistake  the  name  of  Bamberger  instead  of  Stefan  Gambarian.  The 
reference  (Ber.,  41,  3510)  was  correct. 

8  Iy.  Gattermann,  Ber.,  26,  1846  (1893). 


19 

stance.  The  coloration  produced  by  ferric  chloride  is  similar  to  that 
formed  in  the  case  of  the  dimethyl  derivative  and  this  solution  is  decolorized 
by  cone,  hydrochloric  acid.  This  disappearance  of  color  does  not  depend 
upon  the  formation  of  an  acid  salt  but  upon  the  fact  that  the  ferrous  salts 
present  under  these  conditions  reduce  the  quinonimine.  This  equilibrium 
is  again  shifted  when  water  is  added  to  the  solution.  Indeed  the  colora- 
tion produced  by  bromine  is  not  changed  by  cone,  hydrochloric  acid. 

From  solutions  of  the  dihydrochloride  in  water,  the  free  leucobase, 
i.  e.,  the  phenyldiaminophenol,  may  be  precipitated  by  the  addition  of 
alkalies.  The  colorless  crystals  formed  quickly  oxidize  in  the  air  forming  a 
brown  product.  The  leucobase,  insoluble  in  water,  is  soluble  in  strong 
alkalies  and  in  acids. 

V.  Oxidation  of  2-Phenylamino-4-aminophenol.    The  Preparation  of 

o 

II 

/     \. 'M'Trf*  TT 

the  Quinoid  Picrate,  (I      I)  . — On  oxidation  with  ferric  chlo- 

II 

NH.HOCeH2(NO2)8 

ride  this  phenol  gives  a  solution  having  the  same  violet-red  color  as  those 
produced  by  the  phenyldiaminophenol  (IV)  and  the  dimethyldiamino- 
phenol  (II). 

Some  2-phenylamino-4-aminophenol-dihydrochloride  (0.8  g.)  in  40  cc. 
of  50%  acetic  acid  at  o°  was  oxidized  by  2.5  cc.  of  4  N  ferric  chloride.  A 
solution  of  1.2  g.  of  picric  acid  in  16  cc.  of  glacial  acetic  acid  was  added  to 
the  deep  violet  solution.  The  resulting  brownish  solution  was  filtered 
from  a  slight  precipitate.  Then  150  cc.  ice  cold  water  was  run  in  slowly, 
with  stirring,  to  precipitate  the  picrate.  Under  the  microscope  small 
clusters  of  crystals  were  observed.  The  precipitate  was  collected,  washed 
with  cold  dil.  acid  and  finally  with  a  little  ice  cold  water.  It  was  dried  to 
constant  weight.  The  yield  was  75%  of  the  theoretical. 

Subst.,  0.2612;  CO2,  0.4865;  H2O,  o  0752.     Subst.,  0.0852;  12.15  cc.  dry  Na  at  10° 
and  742  mm. 

Calc.  for  Ci8Hi3O8N5:  C,  50.57;  H,  3.07;  N,  16.40.     Found:  C,  50.80;  H,  3.22;  N. 
16.29. 

The  picrate  swells  up  on  being  heated,  evolving  odors  characteristic  of 
picrates,  leaving  a  residue  very  difficult  to  burn.  It  was  necessary  to  re- 
place the  copper  oxide  by  lead  chromate  in  the  determination  of  nitrogen. 

The  picrate  is  scarcely  soluble  in  water,  readily  soluble  in  dilute  acids, 
giving  beautiful  violet  solutions.  It  is  easily  soluble  with  red  color  in 
alcohol,  acetone,  less  soluble  in  chloroform.  In  cone,  sulfuric  acid  an  in- 
tense blue  coloration  is  produced. 

The  salts  of  the  phenylaminoqulnonimine  are  very  unstable  in  solution, 


20 

rapidly  precipitating  a  black  insoluble  substance.  Attempts  to  prepare 
the  salts  of  the  common  inorganic  acids  have  thus  far  failed  due  to  their 
solubility  and  to  rapid  condensations.  Even  in  the  above  picrate  a  small 
residue  insoluble  in  dilute  acids  was  found. 

VI.  Oxidation  of  2,4,6-Triaminophenol.  —  The  diaminoquinonimine 
hydrochloride1  prepared  by  oxidation  of  this  phenol  was  titrated  with 
titanium  trichloride,  the  values  found  agreeing  with  the  assigned  holo- 
quinoid  formula. 

Summary. 

In  the  aminoquinonimine  salts  the  auxochromic  effect  of  one  phenyl- 
amino  group  is,  unlike  the  cases  of  other  holoquinoid  salts,  the  same  as 
the  auxochromic  effect  of  one  dimethylamino  group. 

I  wish  to  express  my  sincere  thanks  for  the  many  helpful  suggestions 
made  by  Dr.  Jean  Piccard,  under  whose  able  direction  this  work  was 
carried  out. 

1  Carl  Heintzel,  Z.  Chem.,  1867,  342. 


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